There's not that much to choose between St Johns Wood and Primrose Hill. I live near Chalk Farm station which is in the Primrose Hill area and love it here. Having this park and Regents Park so near is a blessing.

It takes half an hour to walk to Tottenham Court Road (or to be pushed there in my case) and you can walk down to Baker Street/Marylebone Road just through grass if you like. There's a Saturday farmers market in the area http://www.lfm.org.uk/primrose.asp.

The downside is the proximity to Camden, but once you reach the Roundhouse on Chalk Farm Road it's almost as if it ceases to exist.

I've lived in Hampstead in the past and enjoyed the 'villagey' feel, but I didn't feel so connected to London there. Chalk Farm has been my favourite area to live in London so far (no Tescos - a huge and VERY friendly Morrisons and a small Sainsburies open until 11pm 7 days a week - or you can brave a trip to the mammoth Sainsburies in Camden which is open 24 hours a day except at weekends)